Conflicting overloads with using-declaration

Question

#include <iostream>
struct A {
  void test() { std::cout << "A\n"; }
};
struct B : A {
  void test() { std::cout << "B\n"; }
};
struct C : B {
  using A::test;
  using B::test;
};
int main() {
  C().test();  // Is this ambiguous?
  return 0;
}

In this example, g++ 8.1.0 compiles successfully and calls test() from B.

clang++ 3.8.0 reports: error: call to member function 'test' is ambiguous.

Which is correct? If it is g++, what is the rule that picks B::test over A::test?

This question might help you: https://stackoverflow.com/questions/42573771/why-is-this-call-to-member-function-ambiguous — Trevor Tracy, Jun 13 '18 at 17:27

score 1 · Accepted Answer · answered Jun 13 '18 at 18:52

I believe Clang is correct. According to [namespace.udecl]/13:

Since a using-declaration is a declaration, the restrictions on declarations of the same name in the same declarative region ([basic.scope]) also apply to using-declarations.

Since you can't declare two identical member functions, the same applies to using declarations.

João Paulo · Answer 2 · 2018-06-13T18:55:03.837

0

GCC lets it compile and test() call becomes the first declaration. In the example given, it'll call the A::test(). But ISO C++ defines it as ambiguous. Visual Studio and clang won't let you compile it. Additionally, this the VS error message: 'B::test': ambiguous call to overloaded function. In my opinion, GCC is wrong by letting it compile.

edited Jun 13 '18 at 18:55

answered Jun 13 '18 at 18:35

João Paulo

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Conflicting overloads with using-declaration

2 Answers2